The present invention relates to a two-circuit braking system for motor vehicles employing a lock-prevention device which holds the braking pressure below the locking limit by means of sensors and magnetic valves.
A braking system of this kind is known and disclosed in German Offenlegungsschrift No. 2,038,271. The known braking system has one magnetic inlet valve and one magnetic outlet valve for each braking circuit I and II, and, in addition, has other valve elements which are all susceptible to malfunction as is well known. The correct functioning of a braking system of this kind can be impeded by a fault in the system, for example, by an incorrect switching of the magnetic valves, with the result that a total or a partial failure of the braking system is possible. A failure of the front axle brake is particularly dangerous because without braking capacity at the front wheels, the largest part of the braking capacity of the vehicle is lost because a dynamic load shift to the front axle occurs.